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Subject[tip:x86/signal] x86: signal: check signal stack overflow properly
Commit-ID:  14fc9fbc700dc95b4f46ebd588169324fe6deff8
Gitweb: http://git.kernel.org/tip/14fc9fbc700dc95b4f46ebd588169324fe6deff8
Author: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
AuthorDate: Thu, 19 Mar 2009 10:56:29 -0700
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 20 Mar 2009 19:01:31 +0100

x86: signal: check signal stack overflow properly

Impact: cleanup

Check alternate signal stack overflow with proper stack pointer.
The stack pointer of the next signal frame is different if that
task has i387 state.

On x86_64, redzone would be included.

No need to check SA_ONSTACK if we're already using alternate signal stack.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Cc: Roland McGrath <roland@redhat.com>
LKML-Reference: <49C2874D.3080002@ct.jp.nec.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
arch/x86/kernel/signal.c | 48 +++++++++++++++++++++++++--------------------
1 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index d2cc642..dfcc74a 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -211,31 +211,27 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
{
/* Default to using normal stack */
unsigned long sp = regs->sp;
+ int onsigstack = on_sig_stack(sp);

#ifdef CONFIG_X86_64
/* redzone */
sp -= 128;
#endif /* CONFIG_X86_64 */

- /*
- * If we are on the alternate signal stack and would overflow it, don't.
- * Return an always-bogus address instead so we will die with SIGSEGV.
- */
- if (on_sig_stack(sp) && !likely(on_sig_stack(sp - frame_size)))
- return (void __user *) -1L;
-
- /* This is the X/Open sanctioned signal stack switching. */
- if (ka->sa.sa_flags & SA_ONSTACK) {
- if (sas_ss_flags(sp) == 0)
- sp = current->sas_ss_sp + current->sas_ss_size;
- } else {
+ if (!onsigstack) {
+ /* This is the X/Open sanctioned signal stack switching. */
+ if (ka->sa.sa_flags & SA_ONSTACK) {
+ if (sas_ss_flags(sp) == 0)
+ sp = current->sas_ss_sp + current->sas_ss_size;
+ } else {
#ifdef CONFIG_X86_32
- /* This is the legacy signal stack switching. */
- if ((regs->ss & 0xffff) != __USER_DS &&
- !(ka->sa.sa_flags & SA_RESTORER) &&
- ka->sa.sa_restorer)
- sp = (unsigned long) ka->sa.sa_restorer;
+ /* This is the legacy signal stack switching. */
+ if ((regs->ss & 0xffff) != __USER_DS &&
+ !(ka->sa.sa_flags & SA_RESTORER) &&
+ ka->sa.sa_restorer)
+ sp = (unsigned long) ka->sa.sa_restorer;
#endif /* CONFIG_X86_32 */
+ }
}

if (used_math()) {
@@ -244,12 +240,22 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
sp = round_down(sp, 64);
#endif /* CONFIG_X86_64 */
*fpstate = (void __user *)sp;
-
- if (save_i387_xstate(*fpstate) < 0)
- return (void __user *)-1L;
}

- return (void __user *)align_sigframe(sp - frame_size);
+ sp = align_sigframe(sp - frame_size);
+
+ /*
+ * If we are on the alternate signal stack and would overflow it, don't.
+ * Return an always-bogus address instead so we will die with SIGSEGV.
+ */
+ if (onsigstack && !likely(on_sig_stack(sp)))
+ return (void __user *)-1L;
+
+ /* save i387 state */
+ if (used_math() && save_i387_xstate(*fpstate) < 0)
+ return (void __user *)-1L;
+
+ return (void __user *)sp;
}

#ifdef CONFIG_X86_32

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